We now use threads and other pthread API a lot, and not always we use it
from threads created with pthread_create() (or the main thread). As I
understand, with static linking we would have to use
pthread_win32_thread_attach/detach_np() every time we enter or leave a
foreign thread. We don't do this, and it's not feasible either, so it's
just broken.
This still should work with dynamic pthreads-win32. The MinGW pthread
implementation should be unaffected from all of this.